The present invention relates to the technology of high-power laser application apparatus such as laser machining apparatus and a method of the same. More particularly, the invention relates to laser machining apparatus, laser lithography apparatus, and a method thereof using an excimer laser beam with a wavelength of invisible vacuum ultraviolet rays.
A conventional laser machining apparatus has the observation wavelength made different from the wavelength of the machining laser beam, as described in a Japanese literature "Laser Machining", pp. 84-85, by Susumu Nanba, et al., published on Nov. 30, 1972 by Nikkan Kogyo Shinbun. FIG. 2 is the most simplified illustration of the conventional laser machining apparatus. In the figure, a near infrared light beam with a 1.06 .mu.m wavelength produced by a laser oscillator 31 is reflected by a mirror 32 which reflects the laser and transmits the visible light, and guided to an objective lens 33 by which the laser beam is focused on a work piece 34 placed on a table 35 so that it is machined For the observation of machining, the image of the work piece 34 received by the objective lens 33 is transmitted through the mirror 32 and focused on the operator's eye by an objective lens 36 so that the operator adjusts the laser beam to maintain the machining accuracy.
However, the conventional technique uses different wavelengths for the machining laser beam and observation light, and therefore color matching is needed for the objective lens or a compensation for color matching by some means is required for accurate observation.
Various application techniques of the excimer laser, which include excimer doping of semiconductor, thin film formation and laser fabrication, pertaining to this invention are disclosed in Japanese publication "Machine Tool Series, Laser Machining", pp. 135-154, which is a separate issue of "Applied Mechanics", published on Sep. 10, 1990. The frontier technology of excimer laser is introduced in publication "Precision Engineering" (JSPE), by Ueda, No. 5, pp. 837-840, published in 1989, and the current topics and prospect of submicron lithography based on excimer laser is introduced in "Applied Physics", Vol. 56, No. 9, pp. 44-48, published in 1987.
FIGS. 12 and 13 show examples of conventional laser application apparatus that are illustrated on pages 32 and 33 of "The 5th Laser School Text, B3, Safety of Laser", sponsored by the Optical Industrial Promotion Associates in Japan and the Ministry of Commerce and Industry.
In FIG. 12, a laser beam produced by a CO.sub.2 laser source 81 is guided through a metallic conduit 82 with a thickness of 3 mm or more, reflected in a mirror box 84, and focused on a work piece 85 for machining. A machining chamber 83 is made of acrylic resin with a thickness of 10 mm or more and is designed so that the laser beam does not leak out of the chamber. In FIG. 13, the laser beam produced by a YAG laser source 91 is guided through a metallic conduit with a thickness of 1 mm or more, reflected in a mirror box 94, and focused on a work piece 95 for machining. A machining chamber 93 is made of metal and its interior wall is painted in black. An industrial television camera 96 is provided on the mirror box 94 so that machining is observed on a TV monitor 97.
The conventional techniques shown in FIGS. 12 and 13 have their optical systems enclosed by metallic or acrylic material which does not transmit the light so that the laser beam does not leak out. This arrangement, however, imposes such a problem that the laser blocking wall material which is exposed to the laser beam due to diffraction, scattering or other reason is melted, evaporated and removed and consequently deposited on some important optical part, causing it to be damaged or destroyed when it is hit by the laser beam. This problem is especially serious in the fields of high-power laser machining, laser nuclear fusion and laser energy transmission.